1. Field of the Invention
The present invention relates to a semiconductor device including a semiconductor package with electromagnetic coupling slots, and in particular, to a semiconductor device comprising a high-frequency semiconductor chip mounted on an electromagnetic coupling type semiconductor package, for use at a frequency band equal to or higher than about 1 GHz, namely, a so-called microwave band, a quasi-millimeter wave band and a millimeter wave band. In the present specification, an electrical conductor is referred to as a conductor hereinafter.
2. Description of the Prior Art
FIG. 12 is a sectional view showing a structure of a prior art semiconductor device provided with an electromagnetic coupling type semiconductor package 101a and a high-frequency semiconductor chip 105, FIG. 13 is a plan view showing a top surface of the electromagnetic coupling type semiconductor package 101a of FIG. 12, and FIG. 14 is a bottom view showing a bottom surface of the electromagnetic coupling type semiconductor package 101a of FIG. 12. As shown in FIG. 12, the high-frequency semiconductor chip 105 is mounted on the electromagnetic coupling type semiconductor package 101a.
Referring to FIG. 13, microstrip conductors 102a and 102b are located in the vicinity of ends in the longitudinal direction of a ceramic layer 122 of the electromagnetic coupling type semiconductor package 101a. As shown in FIG. 12, respective microstrip lines L102a and L102b, which respectively serve as high-frequency signal inputting and outputting transmission lines, are constituted by the microstrip conductors 102a and 102b, with the ceramic layer 122 between them, and a grounding conductor 108. Further, as shown in FIG. 12, for the purpose of electromagnetically coupling microstrip lines L106a and L106b on the bottom surface of the electromagnetic coupling type semiconductor package 101a with the microstrip lines L102a and L102b, rectangular slots 103a and 103b, each located by removing a part of the grounding conductor 108, are located on the grounding conductor 108 which is an intermediate layer located between a ceramic layer 121 and the ceramic layer 122 perpendicular to and opposite the microstrip conductors 102a and 102b and microstrip conductors 106a and 106b of the microstrip lines L106a and L106b. In this case, as shown in FIG. 12, the microstrip lines L106a and L106b are constituted by the microstrip conductors 106a and 106b, the ceramic layer 121, and the grounding conductor 108.
Further, the microstrip conductor 102a is electrically connected to one terminal of the high-frequency semiconductor chip 105 by way of a bonding wire 110a, while the microstrip conductor 102b is electrically connected to the other terminal of the high-frequency semiconductor chip 105 by way of a bonding wire 110b. In this case, each of the bonding wires 110a and 10b is made of, for example, an Au wire having a diameter of about 25 .mu.m. The reference numeral 104 denotes a bias conductor for supplying a DC bias voltage to the high-frequency semiconductor chip 105, while the reference numeral 111 denotes a through hole conductor for connecting the grounding conductor 108 to a grounding conductor 107 in the center of the bottom surface of the ceramic layer 121.
In general, the electromagnetic coupling type semiconductor package 110a is formed of a ceramic material such as alumina by a publicly known method including processes of thick film formation, lamination and simultaneous firing. The high-frequency semiconductor chip 105 is die-bonded to the electromagnetic coupling type semiconductor package 101a with a solder material such as AuSn solder, an electrically conductive bonding material or the like.
In the prior art semiconductor device constructed as above, the microstrip line L106a is electromagnetically connected to the microstrip line L102a via the rectangular slot 103a, while the microstrip line L102a is electrically connected to the high-frequency semiconductor chip 105 via the bonding wire 110a. On the other hand, the microstrip line L106b is electromagnetically connected to the microstrip line L102b via the rectangular slot 103b, while the microstrip line L102b is electrically connected to the high-frequency semiconductor chip 105 via the bonding wire 110b. Therefore, for example, a high-frequency signal inputted to the microstrip line L106a is inputted to the high-frequency semiconductor chip 105 via the rectangular slot 103a, the microstrip line L102a and the bonding wire 110a. Then, the inputted high-frequency signal is subjected to the processes of amplification and so on, and the high-frequency signal outputted subsequently is outputted from the high-frequency semiconductor chip 105 to the microstrip line L106b via the bonding wire 110b, the microstrip line L102b and the rectangular slot 103b.
FIG. 15 is a graph showing a high-frequency transmission characteristic of the semiconductor device shown in FIGS. 12 to 14. As is apparent from FIG. 15, the semiconductor device has a transmission loss equal to or smaller than 3 dB in a band ranging from 40 GHz to 60 GHz, and the semiconductor device can be used in this band. In the high-frequency transmission band of the semiconductor device, a desired band can be obtained by adjusting the widths and lengths of the rectangular slots 103a and 103b, the length of each stub or the like.
In the case of this prior art semiconductor device employing the electromagnetic coupling type semiconductor package 110a, the high-frequency semiconductor chip 1 and the semiconductor package 101a are connected to each other by way of the bonding wires 110a and 10b. Therefore, inductance components of the bonding wires 110a and 10b operate as resistance components respectively in the high-frequency region of the quasimillimeter wave band and the millimeter wave band, and this leads to increase in the loss of the high-frequency transmission signal. Furthermore, the bonding wires 110a and 110b cannot control the line impedance as a high-frequency signal transmission line, and therefore, there is such a problem that a reflection loss due to an impedance mismatching with the high-frequency transmission line increases between the high-frequency semiconductor chip 1 and the semiconductor package 101a. Furthermore, the electromagnetic coupling portions of the rectangular slots 103a and 103b allow signals to pass through them only in a desired frequency band, and a total reflection occurs in the other frequency bands on the output side of the high-frequency semiconductor chip 1, resulting in the feedback of the signals to side of the high-frequency semiconductor chip 1. Therefore, there is such a problem that a parasitic oscillation is caused.